That would be the American Killifish Association. Other countries have their own killie cabals.
http://www.aka.org/aka/modules/content/index.php?id=2
If you look at their site, under "the fish", "F&EL" is the fish and egg listing. The august one is up right now.
Here's the deal on delivery: standard, live delivery isn't guaranteed from Nov through Mar. Shipping has gone up to $8 in the last couple months, but that's still a lot cheaper than what you pay when buying live-delivery fish through aquabid! This is mostly because killies are "tough" fish that can stand up to shipping.
For instance, Ruth Warner
http://www.geocities.com/killiesbyruth/Availablefish.html
has 24 species of fish available at $8 per pair. You could get 4 different pairs of fish, delivered, for $32 + $9.50 shipping.
One of the other sellers offers 3 pair of A Australe for $25, with $8 shipping for all three pair. But he wants his box back!
A few of the people want you to return their empty box, but an empty box doesn't need to go by priority. The number of sellers varies by month. Sometimes people will give a 50% discount to new AKA members.
You probably wouldn't need to join the AKA to get a couple fish, but it's one of the more informative clubs out there. I ought to re-join, but I really want to get some flightless fruit fly cultures going before I get more killies. Most killies will eat flake food, but I think live ff's make a real difference.